body {
    background: #000000;
    min-height: 100vh;
    padding-top: 70px;
}

.game-container {
    max-width: 800px;
    margin: 0 auto;
    padding: 20px;
}

.game-header {
    text-align: center;
    margin-bottom: 30px;
}

.game-title {
    color: #00d4ff;
    font-size: 3em;
    font-weight: bold;
    text-shadow: 0 0 20px rgba(0, 212, 255, 0.5);
    margin-bottom: 10px;
}

.game-subtitle {
    color: #ffffff;
    font-size: 1.2em;
    opacity: 0.8;
}

.game-panel {
    background: linear-gradient(135deg, #16213e 0%, #0f3460 100%);
    border-radius: 15px;
    padding: 30px;
    box-shadow: 0 10px 40px rgba(0, 212, 255, 0.2);
}

.difficulty-selector {
    text-align: center;
    margin-bottom: 25px;
}

.difficulty-selector h3 {
    color: #ffffff;
    margin-bottom: 15px;
}

.btn-difficulty {
    background: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);
    border: 2px solid rgba(0, 212, 255, 0.3);
    color: #00d4ff;
    padding: 10px 20px;
    margin: 0 5px;
    border-radius: 10px;
    transition: all 0.3s ease;
}

.btn-difficulty:hover {
    background: linear-gradient(135deg, #16213e 0%, #0f3460 100%);
    border-color: #00d4ff;
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(0, 212, 255, 0.3);
}

.btn-difficulty.active {
    background: linear-gradient(135deg, #00d4ff 0%, #0099ff 100%);
    border-color: #00d4ff;
    color: #0f0f1e;
    box-shadow: 0 5px 15px rgba(0, 212, 255, 0.5);
}

.board-container {
    display: flex;
    justify-content: center;
    margin-bottom: 25px;
}

.sudoku-board {
    border-collapse: collapse;
    background: #0f0f1e;
    border: 3px solid #00d4ff;
    border-radius: 10px;
    overflow: hidden;
}

.sudoku-board td {
    width: 50px;
    height: 50px;
    text-align: center;
    border: 1px solid rgba(0, 212, 255, 0.2);
    position: relative;
    transition: all 0.3s ease;
}

.sudoku-board td:nth-child(3),
.sudoku-board td:nth-child(6) {
    border-right: 2px solid #00d4ff;
}

.sudoku-board tr:nth-child(3) td,
.sudoku-board tr:nth-child(6) td {
    border-bottom: 2px solid #00d4ff;
}

.sudoku-board input {
    width: 100%;
    height: 100%;
    border: none;
    background: transparent;
    color: #00d4ff;
    font-size: 1.5em;
    font-weight: bold;
    text-align: center;
    outline: none;
    cursor: pointer;
}

.sudoku-board input:disabled {
    color: #ffffff;
    cursor: default;
}

.sudoku-board td:hover {
    background: rgba(0, 212, 255, 0.1);
}

.sudoku-board td.selected {
    background: rgba(0, 212, 255, 0.3);
    box-shadow: inset 0 0 10px rgba(0, 212, 255, 0.5);
}

.sudoku-board td.error {
    background: rgba(255, 51, 102, 0.3);
    animation: shake 0.5s;
}

.sudoku-board td.correct {
    background: rgba(0, 255, 136, 0.3);
    animation: pulse 0.5s;
}

.sudoku-board td.hint {
    background: rgba(255, 204, 0, 0.3);
    animation: glow 1s;
}

.number-pad {
    margin-bottom: 25px;
}

.number-pad h4 {
    color: #ffffff;
    text-align: center;
    margin-bottom: 15px;
}

.number-buttons {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 10px;
    max-width: 500px;
    margin: 0 auto;
}

.number-btn {
    background: linear-gradient(135deg, #00d4ff 0%, #0099ff 100%);
    border: none;
    color: #0f0f1e;
    padding: 15px;
    font-size: 1.2em;
    font-weight: bold;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: 0 5px 15px rgba(0, 212, 255, 0.3);
}

.number-btn:hover {
    transform: translateY(-3px);
    box-shadow: 0 7px 20px rgba(0, 212, 255, 0.5);
}

.number-btn:active {
    transform: translateY(-1px);
}

.number-btn.selected {
    background: linear-gradient(135deg, #00ff88 0%, #00cc66 100%);
    box-shadow: 0 5px 15px rgba(0, 255, 136, 0.5);
}

.erase-btn {
    background: linear-gradient(135deg, #ff3366 0%, #ff0044 100%);
    grid-column: span 2;
}

.erase-btn:hover {
    box-shadow: 0 7px 20px rgba(255, 51, 102, 0.5);
}

.game-controls {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 10px;
}

.game-controls .btn {
    padding: 12px;
    font-size: 1em;
    font-weight: bold;
    border-radius: 10px;
    border: none;
    transition: all 0.3s ease;
}

.game-controls .btn-primary {
    background: linear-gradient(135deg, #00d4ff 0%, #0099ff 100%);
    color: #0f0f1e;
    box-shadow: 0 5px 15px rgba(0, 212, 255, 0.3);
}

.game-controls .btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 7px 20px rgba(0, 212, 255, 0.5);
}

.game-controls .btn-success {
    background: linear-gradient(135deg, #00ff88 0%, #00cc66 100%);
    color: #0f0f1e;
    box-shadow: 0 5px 15px rgba(0, 255, 136, 0.3);
}

.game-controls .btn-success:hover {
    transform: translateY(-2px);
    box-shadow: 0 7px 20px rgba(0, 255, 136, 0.5);
}

.game-controls .btn-warning {
    background: linear-gradient(135deg, #ffcc00 0%, #ff9900 100%);
    color: #0f0f1e;
    box-shadow: 0 5px 15px rgba(255, 204, 0, 0.3);
}

.game-controls .btn-warning:hover {
    transform: translateY(-2px);
    box-shadow: 0 7px 20px rgba(255, 204, 0, 0.5);
}

.game-controls .btn-info {
    background: linear-gradient(135deg, #9966ff 0%, #6633ff 100%);
    color: #ffffff;
    box-shadow: 0 5px 15px rgba(153, 102, 255, 0.3);
}

.game-controls .btn-info:hover {
    transform: translateY(-2px);
    box-shadow: 0 7px 20px rgba(153, 102, 255, 0.5);
}

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-5px); }
    75% { transform: translateX(5px); }
}

@keyframes pulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.05); }
}

@keyframes glow {
    0%, 100% { box-shadow: inset 0 0 10px rgba(255, 204, 0, 0.5); }
    50% { box-shadow: inset 0 0 20px rgba(255, 204, 0, 0.8); }
}

@media (max-width: 768px) {
    .game-title {
        font-size: 2em;
    }

    .sudoku-board td {
        width: 35px;
        height: 35px;
    }

    .sudoku-board input {
        font-size: 1.2em;
    }

    .number-buttons {
        grid-template-columns: repeat(3, 1fr);
    }

    .game-controls {
        grid-template-columns: 1fr;
    }
}